This invention relates to a method and apparatus for feeding and registering continuous form paper to a processing unit such an offset press and to a method and apparatus for adapting a processing unit such as an offset press, originally adapted to process single sheets of paper, to process continuous form paper.
The arrival of the word processors and high speed, computer controlled printers in modern offices and businesses have created a need for a variety of business documents, such as invoices, purchaser orders, letterhead, envelopes, checks, and the like to be available on continuous form paper so they may be rapidly processed by the high speed office printer. One method of providing such a capability is to mount the business documents such as letterhead or invoices onto continuous carrier paper. This involves several processes, first the business document must be printed, and second it must be mounted on the carrier paper precisely aligned and registered so that the high speed office printer, which is referenced to the carrier paper through the pin holes on the margins of the carrier paper, will know where to print and where to not print. Expensive, relatively slow machines are needed to mount the documents on the carrier paper in precise registry.
Another method is to print the business documents such as letterhead or invoices directly onto the continuous form paper and then, through the use of perforations in the continuous form paper, separate the printed documents from the marginal strips having the pin holes therein and from the adjacent printed documents. This process is preferable to the carrier mounted method since it eliminates a step and an expensive machine, but it has the same requirement for precise registry. The printing on the continuous form must be precisely placed with respect to the perforations which define the separate documents within the continuous form paper. Lack of proper registration can cause printing to run over the perforations extending across the continuous form paper which define the separate documents.
Printing on continuous form raises another problem, especially in the case of letterhead which should have an "clean edge" appearance and not display detectable serrations on the edges. While perforation methods and apparatus are available which can achieve such a clean edge appearance when the individual sheets of letterhead are broken out of the continuous form, such clean edge perforations are very delicate and prone to breaking during processing.
This then defines the problem, to feed and precisely register continuous form paper to a press or other processing unit without breaking the perforations, even clean edge perforations.
Most of the existing machines for processing continuous form paper use a "tractor feed" device, a system of multiple driven pin wheels or pin belts which engage the pin holes on the margins of the continuous form paper and pull the paper through the processor. Similarly, most of these machines also use the tractor feed mechanism to index or register the continuous form paper to the press or processor. In many processors, such as offset presses and perforators, it is necessary to stop, retard, or advance the passage of paper through the processor to keep the paper in proper registry with the printing or perforating cylinder.
Several disadvantages associated with this type of system are that each of the tractor feed drives on a particular unit must be synchronized and timed with respect to each other and to the processing unit, and that any imprecision in the feeding system is carried over into the registration system. Thus small errors can, with sufficient iterations, accumulate into large errors. Furthermore, the stopping, starting, retarding and advancing of the multiple tractor feed devices, all of which engage the paper, has a tendancy to distort or rip the pin holes, or break the perforations, especially clean edge types of perforations.